Distance-measuring device with increased signal-to-noise ratio and method thereof

ABSTRACT

A method of increasing signal-to-noise ratio of a distance-measuring device includes a light-emitting component emitting a detecting light to a measured object during an emitting period for generating a reflected light, a delay period after the light-emitting component emitting the detecting light, a light-sensing component sensing the energy of the reflected light to generate a light-sensing signal, and obtaining a measured distance between the distance-measuring device and the measured object according to the energy of the detecting light and the light-sensing signal. Since the measured distance is longer than a predetermined shortest measured distance, the method can accordingly calculate a proper delay period for ensuring that the reflected light reaches the light-sensing component after the delay period. In this way, the light-sensing component does not sense the background light during the delay period, so that the signal-to-noise ratio of the light-sensing signal is improved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 12/817,172, filed on Jun. 16, 2010, the contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a distance-measuring device, and more particularly, to distance-measuring device with increased signal-to-noise ratio and method thereof.

2. Description of the Prior Art

In the prior art, the distance-measuring device emits a detecting light to a measured object, and receives the reflected light generated by the measured object reflecting the detecting light. The distance-measuring device calculates the distance between the distance-measuring device and the measured object by means of measuring the period of the detecting light going back and forth between the distance-measuring device and the measured object. However, when the reflectivity of the surface of the measured object is lower, the energy of the reflected light generated by the measured object is lower as well. Thus, the distance-measuring device is easily affected by the background light (noise) so that the distance-measuring device may obtain an incorrect measured distance.

SUMMARY OF THE INVENTION

The present invention provides a method of increasing signal-to-noise ratio of a distance-measuring device. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device has a light-emitting component for emitting a detecting light, and a first light-sensing component for sensing and accumulating energy of light to generate a first light-sensing signal according to a first shutter periodic signal. The method comprises the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period, a delay period after the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the first light-sensing component sensing and accumulating energy of the reflected light to generate the first light-sensing signal, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the first light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period, and obtaining the measured distance according to the time of flight. The delay period is calculated according to the predetermined shorted measured distance for the reflected light reaching the first light-sensing component after the delay period.

The present invention further provides a method of increasing signal-to-noise ratio of a distance-measuring device. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device has a light-emitting component for emitting a detecting light, a first light-sensing component for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and a second light-sensing component for sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The method comprises the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period, a delay period after the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal, switching the second shutter periodic signal to represent turning-on during a second sensing period for the second light-sensing component to sense and accumulate energy of the reflected light to generate the second light-sensing signal when the first light-sensing component stops sensing the reflected light, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal, and obtaining the measured distance according to the time of flight. The delay period is calculated according to the predetermined shorted measured distance for the reflected light reaching the first light-sensing component after the delay period.

The present invention further provides a method of increasing signal-to-noise ratio of a distance-measuring device. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device has a light-emitting component for emitting a detecting light, a light-sensing group for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The method comprises switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component emitting the detecting light to the measured object to generating a reflected light during an emitting period, and not emitting the detecting light during a non-emitting period, a delay period after every time the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal, switching the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal after the first sensing period, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal, and obtaining the measured distance according to the time of flight. The delay period is calculated according to the predetermined shorted measured distance for the reflected light reaching the light-sensing group after the delay period. The light-emitting periodic signal and the first shutter periodic signal are substantially in phase, and a phase of the light-emitting periodic signal is substantially opposite to a phase of the second shutter periodic signal.

The present invention further provides a distance-measuring device with increased signal-to-noise ratio. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device comprises an emitting component, a first light-sensing component, a light-emitting/sensing controlling circuit, and a distance-calculating circuit. The emitting component is utilized for emitting a detecting light. The first light-sensing component is utilized for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal. The light-emitting/sensing controlling circuit is utilized for controlling the emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period. A delay period after the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal representing turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal. The light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance for the reflected light reaching the first light-sensing component after the delay period. The distance-calculating circuit is utilized for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the first light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period, and generating an output signal representing the measured distance according to the time of flight.

The present invention further provides a distance-measuring device with increased signal-to-noise ratio. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device comprises an emitting component, a first light-sensing component, a second light-sensing component, a light-emitting/sensing controlling circuit, and a distance-calculating circuit. The emitting component is utilized for emitting a detecting light. The first light-sensing component is utilized for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal. The second light-sensing component is utilized for sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The light-emitting/sensing controlling circuit is utilized for controlling the emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period. A delay period after the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal representing turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal. When the first light-sensing component stops sensing the reflected light, the light-emitting/sensing controlling circuit switches the second shutter periodic signal representing turning-on during a second sensing period for the second light-sensing component to sense and accumulate energy of the reflected light to generate the second light-sensing signal. The light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance for the reflected light reaching the first light-sensing component after the delay period. The distance-calculating circuit is utilized for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing the measured distance according to the time of flight.

The present invention further provides a distance-measuring device with increased signal-to-noise ratio. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device comprises an emitting component, a light-sensing group, a light-emitting/sensing controlling circuit, and a distance-calculating circuit. The emitting component is utilized for emitting a detecting light. The light-sensing group is utilized for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The light-emitting/sensing controlling circuit is utilized for switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component emitting the detecting light to the measured object to generating a reflected light during an emitting period, and not emitting the detecting light during a non-emitting period. A delay period after every time the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal. After the first sensing period, the light-emitting/sensing controlling circuit switches the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal. The light-emitting periodic signal and the first shutter periodic signal are substantially in phase, and a phase of the light-emitting periodic signal is substantially opposite to a phase of the second shutter periodic signal. The light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance for the reflected light reaching the first light-sensing component after the delay period. The distance-calculating circuit is utilized for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing the measured distance according to the time of flight.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a distance-measuring device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of the control signals of the distance-measuring device in the “background-measuring phase”.

FIG. 3 is a waveform diagram of the control signals of the distance-measuring device in the “distance-calculating phase”.

FIG. 4 is a waveform diagram of the control signals of the distance-measuring device in the “frequency-adjusting phase”.

FIG. 5 is a diagram illustrating a distance-measuring device according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating the driving circuit generating the control signals, according to the shutter periodic signals and the reading signal.

FIG. 7 is a diagram illustrating the structure of the light-sensing group according to an embodiment of the present invention.

FIG. 8 is a diagram illustrating a distance-measuring device according to a third embodiment of the present invention.

FIG. 9 is a diagram illustrating the structure of the light-sensing group according to an embodiment of the present invention.

FIG. 10 and FIG. 11 are diagrams illustrating a 3D image-sensing device of the present invention.

FIG. 12, FIG. 13, FIG. 14, and FIG. 15 are diagrams illustrating a method of increasing signal-to-noise ratio of a distance-measuring device according to an embodiment of the present invention.

FIG. 16, FIG. 17, FIG. 18, and FIG. 19 are diagrams illustrating a method of increasing signal-to-noise ratio of a distance-measuring device according to another embodiment of the present invention.

FIG. 20, and FIG. 21 are diagrams illustrating a method of increasing signal-to-noise ratio of the distance-measuring device of FIG. 1 according to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1. FIG. 1 is a diagram illustrating a distance-measuring device 100 according to a first embodiment of the present invention. The distance-measuring device 100 is utilized for measuring the measured distance D, wherein the measured distance D is the distance between the measured object O₁ and the distance-measuring device 100, as shown in FIG. 1. The distance-measuring device 100 comprises a light-emitting/sensing controlling circuit 110, a light-emitting component 120, a light-sensing group 130, a distance-calculating circuit 140, a background-calculating circuit 150, a frequency-adjusting circuit 160, and a focusing module 170.

The light-emitting/sensing controlling circuit 110 is utilized for generating a light-emitting periodic signal S_(LD), shutter periodic signals S_(ST1) and S_(ST2), a phase signal S_(P), a frequency-detecting signal S_(FQ), and a reading signal S_(RE). The light-emitting periodic signal S_(LD), and the shutter periodic signals S_(ST1) and S_(ST2) have the same frequency. The frequency-detecting signal S_(FQ) indicates the magnitude of the frequency of the light-emitting periodic signal S_(LD), and the shutter periodic signals S_(ST1) and S_(ST2), which means when a device receives the frequency-detecting signal S_(FQ), the device obtains the magnitude of the frequency of the light-emitting periodic signal S_(LD). In addition, the phases of the light-emitting periodic signal S_(LD) and the shutter periodic signal S_(ST1) are approximately the same (in phase), and the phase of the light-emitting periodic signal S_(LD) is approximately opposite to that of the shutter periodic signal S_(ST2).

The light-emitting component 120 may be a Light-Emitting Diode (LED). The light-emitting component 120 emits a detecting light L_(ID) to the measured object O₁ according to the light-emitting periodic signal S_(LD). For example, when the light-emitting periodic signal S_(LD) represents “emitting”, the light-emitting component 120 emits the detecting light L_(ID); otherwise, when the light-emitting periodic signal S_(LD) represents “not-emitting”, the light-emitting component 120 does not emit the detecting light L_(ID).

The focusing module 170 is utilized for focusing the reflected light L_(RD), which is generated by the measured object O₁ reflecting the detecting light L_(ID), to the light-sensing group 130.

The light-sensing group 130 is a Charge Coupled Device (CCD) or a Complementary Metal-Oxide-Semiconductor (CMOS) light sensor. The light-sensing group 130 senses and accumulates the energy of the reflected light L_(RD) according to the shutter periodic signal S_(ST1). In addition, the light-sensing group 130 outputs the light-sensing signal S_(LS1) according to the reading signal S_(RE). For instance, when the shutter periodic signal S_(ST1) represents “turning-on”, the light-sensing group 130 senses the energy of the reflected light L_(RD) so as to accordingly accumulate the energy E_(R1); when the shutter periodic signal S_(ST1) represents “turning-off”, the light-sensing group 130 does not sense the energy of the reflected light L_(RD), and does not accumulate the energy E_(R1). When the reading signal S_(RE) represents “reading”, the light-sensing group 130 outputs the light-sensing signal S_(LS1) according to the accumulated energy E_(R1). Besides, the light-sensing group 130 also senses and accumulates the energy of the reflected light L_(RD) according to the shutter periodic signal S_(ST2), and the light-sensing group 130 outputs the light-sensing signal S_(LS2) according to the reading signal S_(RE) as well. For instance, when the shutter periodic signal S_(ST2) represents “turning-on”, the light-sensing group 130 senses the energy of the reflected light L_(RD) so as to accordingly accumulate the energy E_(R2); when the shutter periodic signal S_(ST2) represents “turning-off”, the light-sensing group 130 does not sense the energy of the reflected light L_(RD), and does not accumulate the energy E_(R2). When the reading signal S_(RE) represents “reading”, the light-sensing group 130 outputs the light-sensing signal S_(LS2) according to the accumulated energy E_(R2). In addition, it is noticeable that after the light-sensing group 130 outputs the light-sensing signals S_(LS1) and S_(LS2) according to the reading signal S_(RE) representing “reading”, the light-sensing group 130 resets the accumulated energy E_(R1) and E_(R2) (which means the light-sensing group 130 releases the accumulated energy E_(R1) and E_(R2))

The background-calculating circuit 150 outputs the background signal S_(B) according to the phase signal S_(P) and the light-sensing signal S_(LS1).

The frequency-adjusting circuit 160 outputs the frequency-controlling signal S_(FC) according to the phase signal S_(P) and the light-sensing signal S_(LS1). The distance-calculating circuit 140 calculates the measured distance D between the measured object O₁ and the distance-measuring device 100 according to the phase signal S_(P), the background signal S_(B), the light-sensing signals S_(LS1) and S_(LS2), and the frequency-detecting signal S_(FQ).

When the distance-measuring device 100 measures the measured distance D, the measuring process includes a “background-measuring phase”, a “frequency-adjusting phase”, and a “distance-calculating phase”. The operation principle of each phase is illustrated in detail as below.

Please refer to FIG. 2. FIG. 2 is a waveform diagram of the control signals of the distance-measuring device 100 in the “background-measuring phase”. When the distance-measuring device 100 enters the “background-measuring phase”, the distance-measuring device 100 measures the energy of the background light L_(B) sensed by the light-sensing group 130 per unit time, so that the distance-measuring device 100 can reduce the effect of the background light L_(B) in the “distance-calculating phase”. At the beginning of the “background-measuring phase”, the light-emitting/sensing controlling circuit 110 generates the reading signal S_(RE) representing “reading” so as to reset the accumulated energy of the light-sensing group 130. Then, the light-emitting/sensing controlling circuit 110 generates the shutter periodic signal S_(ST1) having a pulse width T_(B), wherein T_(B) represents a background-measuring period. Meanwhile, since the light-emitting periodic signal S_(LD) represents “not-emitting”, the light-emitting component 120 does not emit the detecting light L_(ID). Hence, instead of the light-sensing group 130 sensing the energy of the reflected light L_(RD), the light-sensing group 130 only senses the energy of the background light L_(B) so as to accumulate the energy E_(B) corresponding to the background light L_(B). After the background-measuring period T_(B), the shutter periodic signal S_(ST1) change to be “turning-off”. Meanwhile, the light-emitting/sensing controlling circuit 110 simultaneously generates the reading signal S_(RE) representing “reading” and the phase signal Sp representing “background-measuring”, so that the light-sensing group 130 outputs the light-sensing signal S_(LS1) according to the accumulated energy E_(B), and the background-calculating circuit 150 outputs the background signal S_(B) to the distance-calculating circuit 140 according to the frequency-detecting signal S_(FQ) and the light-sensing signal S_(LS1). The value of the background signal S_(B) represents the energy of the background light L_(B) sensed by the light-sensing group 130 per unit time and can be represented as the following formula: S _(B) =E _(B) /T _(B)  (1); wherein E_(B) is the total energy accumulated by the light-sensing group 130 sensing the background light L_(B) in the background-measuring period T_(B).

Please refer to FIG. 3. FIG. 3 is a waveform diagram of the control signals of the distance-measuring device 100 in the “distance-calculating phase”. When the distance-measuring device 100 enters the “distance-calculating phase”, the distance-measuring device 100 controls the light-emitting component 120 emitting the detecting light L_(ID) by means of the light-emitting periodic signal S_(LD) of the detecting frequency F_(C), and the distance-measuring device 100 calculates the period length of the light going back and forth between the measured object O₁ and the distance-measuring device 100, by means of the light-sensing group 130 sensing the energy of the reflected light L_(RD), so as to obtain the measured distance D. At the beginning of the “distance-calculating phase”, the light-emitting/sensing controlling circuit 110 generates the reading signal S_(RE) representing “reading” to reset the accumulated energy of the light-sensing group 130. Then, the light-emitting/sensing controlling circuit 110 generates the shutter periodic signals S_(ST1) and S_(ST2), and the light-emitting periodic signals S_(LD) with the detecting frequency F_(C) in the detecting cycles T_(C1)˜T_(CN). Therefore, in the detecting cycles T_(C1)˜T_(CN), the shutter periodic signals S_(ST1) and S_(ST2) repeat being switched between “turning-on” and “turning-off”, and the light-emitting periodic signals S_(LD) repeats being switched between “emitting” and “not-emitting”. The period length of each detecting cycle T_(C1)˜T_(CN) is equal to a detecting cycle T_(C), wherein the value of the detecting cycle T_(C) is the inverse of the detecting frequency F_(C). In the detecting cycles T_(C1)˜T_(CN), the phases of the light-emitting periodic signal S_(LD) and the shutter periodic signal S_(ST1) are approximately the same (in phase), and the phase of the shutter periodic signal S_(ST1) is opposite to that of the shutter periodic signal S_(ST2). More particularly, in the detecting cycles T_(C1)˜T_(CN), when the light-emitting periodic signal S_(LD) represents “emitting”, the shutter periodic signal S_(ST1) represents “turning-on” and the shutter periodic signal S_(ST2) represents “turning-off”; when the light-emitting periodic signal S_(LD) represents “not-emitting”, the shutter periodic signal S_(ST1) represents “turning-off” and the shutter periodic signal S_(ST2) represents “turning-on”. In this way, in the first-half cycles of the detecting cycles T_(C1)˜T_(CN), the light-emitting component 120 emits the detecting light L_(ID) and the light-sensing group 130 senses the energy of the reflected light L_(RD) so as to accumulate the energy E_(R1); and in the second-half cycles of the detecting cycles T_(C1)˜T_(CN), the light-sensing group 130 senses the energy of the reflected light L_(RD) so as to accumulate the energy E_(R2).

After the detecting cycles T_(C1)˜T_(CN), the light-emitting/sensing controlling circuit 110 simultaneously generates the reading signal S_(RE) representing “reading” and the phase signal S_(P) representing “distance-calculating”, so that the light-sensing group 130 outputs the light-sensing signal S_(LS1) to the distance-calculating circuit 140 according to the accumulated energy E_(R1) and E_(B1) and outputs the light-sensing signal S_(LS2) to the distance-calculating circuit 140 according to the accumulated energy E_(R2) and E_(B2), wherein the accumulated energy E_(R1) is generated by the light-sensing group 130 sensing the reflected light L_(RD) in the first-half cycles of the detecting cycles T_(C1)˜T_(CN); the accumulated energy E_(B1) is generated by the light-sensing group 130 sensing the background light L_(B) in the first-half cycles of the detecting cycles T_(C1)˜T_(CN); the accumulated energy E_(R2) is generated by the light-sensing group 130 sensing the reflected light L_(RD) in the second-half cycles of the detecting cycles T_(C1)˜T_(CN); and the accumulated energy Eel is generated by the light-sensing group 130 sensing the background light L_(B) in the second-half cycles of the detecting cycles T_(C1)˜T_(CN). The distance-calculating circuit 140 calculates the measured distance D between the measured object O₁ and the distance-measuring device 100 according the frequency-detecting signal S_(FQ), the light-sensing signals S_(LS1) and S_(LS2), and the background signal Se, wherein the values of the light-sensing signals S_(LS1) and S_(LS2) are respectively equal to (E_(R1)+E_(B1)) and (E_(R2)+E_(B2)), and the value of the frequency-detecting signal S_(FQ) is equal to the detecting frequency F_(C). The operation principle of calculating measured distance D is illustrated as below.

It can be seen in FIG. 3 that a round-trip period T_(D) after the light-emitting component 120 emitting the detecting light L_(ID), the light-sensing group 130 starts to sense the reflected light L_(RD) (that is, the reflected light L_(RD) reaches the light-sensing group 130). In other words, the round-trip period T_(D) is the sum of the period of the detecting light L_(ID) flying from the light-emitting component 120 to the measured object O₁ and the period of the reflected light L_(RD) flying from the measured object O₁ to the light-sensing group (that is, the time the light going back and forth between the measured object O₁ and the distance-measuring device 100). Since the period length of the light-sensing group 130 sensing the reflected light L_(RD) to accumulate energy E_(R1) in the first-half cycle of the detecting cycle T_(C1) is [(T_(C)/2)−T_(D)] and the pulse width of the detecting light L_(ID) is equal to (T_(C)/2), the period length of the light-sensing group 130 sensing the reflected light L_(RD) to accumulate energy E_(R2) in the second-half cycle of the detecting cycle T_(C1) is equal to the period length of the pulse width of the detecting light L_(ID) deducting the period of the light-sensing group 130 sensing the reflected light L_(RD) to accumulate energy E_(R1) in the first-half cycle of the detecting cycle T_(C1). That is, the period length of the light-sensing group 130 sensing the reflected light L_(RD) to accumulate energy E_(R2) in the second-half cycle of the detecting cycle T_(C1) is equal to that of the round-trip period T_(D). In the detecting cycles T_(C1)˜T_(CN), since the light-emitting/sensing controlling circuit 110 generates the light-emitting periodic signal S_(LD), and the shutter periodic signals S_(ST1) and S_(ST2) with the “fixed” detecting frequency F_(C), the period length of the light-sensing group 130 sensing the reflected light L_(RD) to accumulate the energy E_(R1) in each first-half cycle is equal to [(T_(C)/2)−T_(D)], and the period length of the light-sensing group 130 sensing the reflected light L_(RD) to accumulate the energy E_(R2) in each second-half cycle is equal to T_(D). In this way, the ratio between the accumulated energy E_(R1) and E_(R2) is equal to [(T_(C)/2)−T_(D)]/T_(D). As a result, the relation between the round-trip period T_(D), the light-sensing signals S_(LS1) and S_(LS2), the detecting frequency F_(C), and the background signal S_(B) can be represented as the following formula:

$\begin{matrix} \begin{matrix} {T_{D} = {\left( {T_{C}/2} \right) \times \left\lbrack {E_{R\; 2}/\left( {E_{R\; 1} + E_{R\; 2}} \right)} \right\rbrack}} \\ {= {\left\lbrack {1/\left( {2 \times F_{C}} \right)} \right\rbrack \times \left\lbrack {\left( {S_{{LS}\; 2} - E_{B\; 2}} \right)/\left( {S_{{LS}\; 1} - E_{B\; 1} + S_{{LS}\; 2} - E_{B\; 2}} \right)} \right\rbrack}} \\ {= {\left\lbrack {1/\left( {2 \times F_{C}} \right)} \right\rbrack \times \left\lbrack {\left( {S_{{LS}\; 2} - E_{B\; 2}} \right)/\left( {S_{{LS}\; 1} - E_{B\; 1} + S_{{LS}\; 2} - E_{B\; 2}} \right)} \right\rbrack}} \\ {= {\left\lbrack {1/\left( {2 \times F_{C}} \right)} \right\rbrack \times}} \\ {\left\lbrack {\left( {S_{{LS}\; 2} - {S_{B}/\left( {2 \times F_{C}} \right)}} \right)/\left( {S_{{LS}\; 1} + S_{{LS}\; 2} - {S_{B}/F_{C}}} \right)} \right\rbrack;} \end{matrix} & (2) \end{matrix}$ since the round-trip period T_(D) is the time of the light going back and forth between the measured object O₁ and the distance-measuring device 100, the measured distance D can be represented as the following formula:

$\begin{matrix} \begin{matrix} {D = {T_{D} \times {C/2}}} \\ {= {\left\lbrack {C/\left( {4 \times F_{C}} \right)} \right\rbrack \times}} \\ {\left\lbrack {\left( {S_{{LS}\; 2} - {S_{B}/\left( {2 \times F_{C}} \right)}} \right)/\left( {S_{{LS}\; 1} + S_{{LS}\; 2} - {S_{B}/F_{C}}} \right)} \right\rbrack;} \end{matrix} & (3) \end{matrix}$ wherein C represents the light speed, N represents the number of the detecting cycles in the “distance-calculating phase”.

In addition, it is noticeable, in the “distance-calculating phase”, when N is equal to 1, it means the light-sensing group 130 senses the reflected light L_(RD) in only one detecting cycle to accumulate the energy E_(R1) and E_(R2). However, if the reflectivity of the measured object O₁ is lower or the measured distance D is longer, the energy of the reflected light L_(RD) becomes lower. In this way, the accumulated energy E_(R1) and E_(R2) of the light-sensing group 130 is so small that the measuring error may become too large to cause the distance-measuring device 100 obtains an incorrect measured distance. When N becomes larger, the light-sensing group 130 senses the reflected light L_(RD) in more detecting cycles to accumulate the energy E_(R1) and E_(R2), so that the energy E_(R1) and E_(R2) becomes larger. In this case, even if the reflectivity of the measured object O₁ is lower or the measured distance D is longer, the accumulated energy still can be raised up to be large enough by increasing the number of the detecting cycles, so that the measuring error can be reduced.

In addition, in the “distance-calculating phase”, the measured distance D is calculated according to the round-trip period T_(D) of the formula (2). However, if the measured distance D between the distance-measuring device 100 and the measured object O₁ is too long, it may causes the round-trip period T_(D) is longer than a half of the detecting cycle T_(C). That is, in the first-half cycle of the detecting cycle T_(C1), the light-sensing group does not sense the reflected light L_(RD) to accumulate the energy E_(R1). In this way, the ratio between the accumulated energy E_(R1) and E_(R2) is not equal to [(T_(C)/2)−T_(D)]/T_(D), so that the distance-calculating circuit 140 can not correctly calculate the measured distance D according to the formula (3). Consequently, the present invention provide a method (“frequency-adjusting phase”) for the distance-measuring device 100 adjusting the detecting cycle T_(C) (or the detecting frequency F_(C)) before the “distance-calculating phase”, so as to assure that the round-trip period T_(D) is shorter than a half of the detecting cycle T_(C) and the distance-calculating circuit 140 can correctly calculate the measured distance D according to the formula (3).

Please refer to FIG. 4. FIG. 4 is a waveform diagram of the control signals of the distance-measuring device 100 in the “frequency-adjusting phase”. As shown in the left part of FIG. 4, when the distance-measuring device 100 enters the “frequency-adjusting phase”, the light-emitting/sensing controlling circuit 110 generates the reading signal S_(RE) representing “reading” so as to reset the accumulated energy of the light-sensing group 130. After that, the light-sensing/emitting controlling circuit 110 simultaneously generates the light-emitting periodic signal S_(LD), which is representing “emitting” and having a pulse width (T_(C)/2), and the shutter periodic signal S_(ST1), which is representing “turning-on” and having a pulse width (T_(C)/2). Finally, the light-emitting/sensing controlling circuit 110 generates the reading signal S_(RE) representing “reading” and the phase signal S_(P) representing “frequency-adjusting”, so that the light-sensing group 130 outputs the light-sensing signal S_(LS1) according to the energy E_(R) accumulated by the light-sensing group 130 sensing the reflected light L_(RD) and the energy E_(B) accumulated by light-sensing group 130 sensing the background light L_(B) (more particularly, S_(LS1)=E_(B)+E_(R)). The frequency-adjusting circuit 160 outputs the frequency-controlling signal S_(FC) according to the light-sensing signal S_(LS1) and the background signal S_(B). It can be seen in FIG. 4 that when the round-trip period T_(D) of the light going back and forth between the distance-measuring device 100 and the measured object O₁ is shorter than (T_(C)/2), it means that the reflected light L_(RD) can reach the light-sensing group 130 before the end of the period of the shutter periodic signal S_(ST1) representing “turning-on”. Therefore, the light-sensing group 130 can sense the reflected light L_(RD) so as to accumulate the energy E_(R). When the round-trip period T_(D) is longer than (T_(C)/2), it means that the reflected light L_(RD) can not reach the light-sensing group 130 in time. Thus, the light-sensing group 130 can not sense the reflected light L_(RD) and can not accumulate the energy E_(R). In addition, the energy E_(R) can be represented as the following formula: E _(R) =S _(LS1) −S _(B)/(2×F _(C))  (4); hence, when the frequency-adjusting circuit 160 determines that the accumulated energy E_(R) is smaller or equal to a predetermined threshold energy E_(TH) (for example, E_(TH) is zero) according to formula (4), it means the round-trip period T_(D) is longer than (T_(C)/2) and the reflected light L_(RD) can not reach the light-sensing group 130 in time. Meanwhile, the frequency-adjusting circuit 160 outputs the frequency-controlling signal S_(FC) representing “reducing” so as to control the light-emitting/sensing controlling circuit 110 reducing the detecting frequency F_(C) (that is, increasing the detecting cycle T_(C)). After the light-emitting/sensing controlling circuit 110 reduces the detecting frequency F_(C), The light-emitting/sensing controlling circuit 110 repeats the above-mentioned process again to determine if the round-trip period T_(D) is shorter than (T_(C)/2) (that is, the reflected light L_(RD) can reach the light-sensing group 130 in time). When the frequency-adjusting circuit 160 determines the accumulated energy E_(R) is larger than the predetermined threshold energy E_(TH), it represents that the round-trip period T_(D) is shorter than (T_(C)/2). Meanwhile, the frequency 160 outputs the frequency-controlling signal F_(C) representing “maintaining” so as to control the light-emitting/sensing controlling circuit 110 keeping the detecting frequency F_(C) unchanged and finish the “frequency-adjusting phase”. In this way, the device-measuring device 100 assures the round-trip period T_(D) is shorter than (T_(C)/2) (that is, the reflected light L_(RD) can reach the light-sensing group 130 in time) by means of the frequency-adjusting circuit 160 adjusting the detecting frequency F_(C) in the “frequency-adjusting phase”.

In conclusion, In the “background-measuring phase”, the light-sensing group 130 senses the background light L_(B), so that the distance-measuring device 100 can calculates the energy accumulated by the light-sensing group 130 sensing the background light L_(B) per unit time; In the “frequency-adjusting phase”, the distance-measuring device 100 reduces the detecting frequency F_(C) until the round-trip period T_(D) is shorter than (T_(C)/2) (that is, the reflected light L_(RD) can reach the light-sensing group 130 in time); in the “distance-calculating phase” the distance-measuring device 100 calculates the measured distance D, by means of the formula (3), according to the background signal S_(B), the frequency-detecting signal S_(FQ), and the light-sensing signals S_(LS1) and S_(LS2), which are outputted by the light-sensing group 130 sensing the reflected light in detecting cycles T_(C1)˜T_(CN). The distance-measuring device 100 calibrates the ratio between the light-sensing signals S_(LS1) and S_(LS2) according to the background signal S_(B). In this way, the distance-measuring device 100 reduces the effect of the background light L_(B) and the measuring error when the measured distance D is too long or when the reflectivity of the measured object O₁ is too low, so that the distance-measuring device 100 can more correctly calculate the measured distance D.

Please refer to FIG. 5. FIG. 5 is a diagram illustrating a distance-measuring device 500 according to a second embodiment of the present invention. The structure and the operation principle of the light-emitting/sensing controlling circuit 511, the light-emitting component 520, the distance-calculating circuit 540, the background-calculating circuit 550, the frequency-adjusting circuit 560, and the focusing module 570 are respectively similar to those of the light-emitting/sensing controlling circuit 110, the light-emitting component 120, the distance-calculating circuit 140, the background-calculating circuit 150, the frequency-adjusting circuit 160, and the focusing module 170, and will not be repeated again for brevity. Compared with the distance-measuring device 100, the distance-measuring device 500 comprises a light-emitting/sensing module 510. The light-emitting/sensing module 510 includes the light-emitting/sensing controlling circuit 511, and a driving circuit 512. The driving circuit 512 generates shutter-on pulse signals S_(SOP1) and S_(SOP2), shutter-off pulse signals S_(SCP1) and S_(SCP2), reset pulse signals S_(RP1) and S_(RP2), and output pulse signals S_(SCP1) and S_(SCP2) according to the shutter periodic signals S_(ST1) and S_(ST2), and the reading signal S_(RE). The light-sensing group 530 comprises light-sensing components 531 and 532. The light-sensing component 531 senses the background light L_(B) or the reflected light L_(RD) to accumulate the energy according to the shutter-on pulse signal S_(SOP1), and the shutter-off pulse signal S_(SCP1); the light-sensing component 531 outputs the light-sensing signal S_(LS1) according to the output pulse signal S_(OP1) and the accumulated energy; and the light-sensing component 531 resets the accumulated energy according to the reset pulse signal S_(RP1). Similarly, the light-sensing component 532 senses the background light L_(B) or the reflected light L_(RD) to accumulate the energy according to the shutter-on pulse signal S_(SOP2), and the shutter-off pulse signal S_(SCP2); the light-sensing component 532 outputs the light-sensing signal S_(LS2) according to the output pulse signal S_(OP2) and the accumulated energy; and the light-sensing component 532 resets the accumulated energy according to the reset pulse signal S_(RP2).

Please refer to FIG. 6. FIG. 6 is a diagram illustrating the driving circuit 512 generating the shutter-on pulse signals S_(SOP1) and S_(SOP2), the shutter-off pulse signals S_(SCP1) and S_(SCP2), the reset pulse signals S_(RP1) and S_(RP2), and the output pulse signals S_(OP1) and S_(OP2) according the shutter periodic signals S_(ST1) and S_(ST2), and the reading signal S_(RE). As shown in FIG. 6, when the shutter periodic signal S_(ST1) changes from “turning-off” to “turning-on”, the driving circuit 512 generates the shutter-on pulse signal S_(SOP1); when the shutter periodic signal S_(ST1) changes from “turning-on” to “turning-off”, the driving circuit 512 generates the shutter-off pulse signal S_(SCP1). When the shutter periodic signal S_(ST2) changes from “turning-off” to “turning-on”, the driving circuit 512 generates the shutter-on pulse signal S_(SOP2), when the shutter periodic signal S_(ST2) changes from “turning-on” to “turning-off”, the driving circuit 512 generates the shutter-off pulse signal S_(SOP2). When the reading signal S_(RE) represents “reading”, the driving circuit 512 generates the output pulse signals S_(OP1) and S_(OP2), and then generates the reset pulse signals S_(RP1) and S_(RP2).

Please refer to FIG. 7. FIG. 7 is a diagram illustrating the structure of the light-sensing group 530 according to an embodiment of the present invention. The structure of the light-sensing group 530 is similar to that of the CMOS light sensor of the digital camera. The light-sensing component 531 comprises switches SW₁₁, SW₁₂, SW₁₃ and SW₁₄, a photo diode PD₁, a capacitor C₁, and a transistor Q₁. When the control end C of the switch SW₁₃ receives the reset pulse signal S_(RP1), the first end 1 of the switch SW₁₃ is couple to the second end 2 of the switch SW₁₃ (which means the switch SW₁₃ is turned on), so that the capacitor C₁ is couple to the voltage source V_(DD) through the turned-on switch SW₁₃ to reset the voltage V_(C1) to be at a predetermined voltage level (for instance, V_(DD)). The photo diode PD₁ is utilized for generating and accumulating electrons of a quantity N_(E1) according to the energy of the reflected light L_(RD). When the control end C of the switch SW₁₂ receives the shutter-off pulse signal S_(SCP1), the first end 1 of the switch SW₁₂ is couple to the second end 2 of the switch SW₁₂ (which means the switch SW₁₂ is turned on), so that the accumulated electrons of the photo diode PD₁ flows to the capacitor C₁, reducing the voltage V_(C1). The switch SW₁₁ is utilized for eliminating the residual electrons of the photo diode PD₁ according to the shutter-on pulse signal S_(SOP1) so as to reset the electron quantity N_(E1). More particularly, when the control end C of the switch SW₁₁ receives the shutter-on pulse signal S_(SOP1), the first end 1 of the switch SW₁₁ is coupled to the second end 2 of the switch SW₁₁, so that the photo diode PD₁ is coupled to the voltage source V_(DD) through the turned-on switch SW₁₁ and the accumulated electrons of the photo diode PD₁ flow to the voltage source V_(DD) through the turned-on switch SW₁₁. The transistor Q₁ is utilized as a voltage follower. As a result, the voltage on the second end 2 of the transistor Q₁ varies with the voltage (V_(C1)) on the control end (gate) C of the transistor Q₁. When the control end C of the switch SW₁₄ receives the output pulse signal S_(OP1), the first end 1 and the second 2 of the switch SW₁₄ are coupled together. Therefore, the switch SW₁₄ outputs the light-sensing signal S_(LS1) according to the voltage V_(C1) by means of the transistor Q₁ (voltage follower). In this way, the voltage V_(C1) can be obtained according to the light-sensing signal S_(LS1), and the accumulated energy of the light-sensing component 531 can be calculated according to the voltage difference between voltage level of the voltage V_(C1) and the predetermined voltage level (for example, V_(DD)).

The light-sensing component 532 comprises switches SW₂₁, SW₂₂, SW₂₃ and SW₂₄, a photo diode PD₂, a capacitor C₂, and a transistor Q₂. The structure and the operation principle of the light-sensing component 532 are similar to those of the light-sensing component 531, and are omitted for brevity.

When the light-emitting/sensing controlling circuit 511 generates the shutter periodic signals S_(ST1) or S_(ST2), or the reading signal S_(RE), the driving circuit 512 accordingly generates the corresponding control signals (the shutter-on pulse signals S_(SOP1) and S_(SOP2), shutter-off pulse signals S_(SCP1) and S_(SCP2), reset pulse signals S_(RP1) and S_(RP2), and output pulse signals S_(OP1) and S_(OP2)) to control the light-sensing components 531 and 532 of the light-sensing group 530. More particularly, when the shutter periodic signal S_(ST1) represents “turning-on”, the light-sensing component 531 senses the energy of the reflected light L_(RD); when the shutter periodic signal S_(ST2) represents “turning-on”, the light-sensing component 532 senses the energy of the reflected light L_(RD). When the reading signal S_(RE) represents “reading”, the light-sensing component 531 outputs the light-sensing signal S_(LS1) and resets the accumulated energy of the light-sensing component 531 at the same time, and the light-sensing component 532 outputs the light-sensing signal S_(LS2) and resets the accumulated energy of the light-sensing component 532 at the same time. In other words, by means of the driving circuit 512, the light-sensing group 530 can operate as the light-sensing group 130 and the distance-measuring device 500 can operate as the distance-measuring device 100 as well. Consequently, the distance-measuring 500 can correctly measure the measured distance D by means of the methods of the “background-measuring phase”, the “frequency-adjusting phase”, and the “distance-calculating phase” mentioned in FIG. 2˜FIG. 4.

Please refer to FIG. 8. FIG. 8 is a diagram illustrating a distance-measuring device 800 according to a third embodiment of the present invention. The structure and the operation principle of the light-emitting/sensing controlling circuit 811, the light-emitting component 820, the distance-calculating circuit 840, the background-calculating circuit 850, the frequency-adjusting circuit 860, and the focusing module 870 are respectively similar to those of the light-emitting/sensing controlling circuit 110, the light-emitting component 120, the distance-calculating circuit 140, the background-calculating circuit 150, the frequency-adjusting circuit 160, and the focusing module 170, and will not be repeated again for brevity. The light-emitting/sensing module 810 comprises the light-emitting/sensing controlling circuit 811, and a driving circuit 812. The driving circuit 812 generates the shutter-on pulse signal S_(SOP), the shutter-off pulse signals S_(SCP1) and S_(SCP2), the reset pulse signals S_(RP1) and S_(RP2), and the output pulse signals S_(SCP1) and S_(OP2) according to the shutter periodic signals S_(ST1) and S_(ST2), and the reading signal S_(RE). The operation principle of the driving circuit 812 is similar to that of the driving circuit 512. The difference between the driving circuits 512 and 812 is that no matter when the shutter periodic signal S_(ST1) or the shutter periodic signal S_(ST2) changes from “turning-off” to “turning-on”, the driving circuit 812 triggers the shutter-on pulse signal S_(SOP).

Please refer to FIG. 9. FIG. 9 is a diagram illustrating the structure of the light-sensing group 830 according to an embodiment of the present invention. The structure and the operation principle of the light-sensing group 830 are similar to those of the light-sensing group 530. Compared with the light-sensing group 530, the light-sensing group 830 does not have the switch SW₂₁ and the photo diode PD₂. Since in the “background-measuring phase” or in the “frequency-adjusting phase”, the distance-measuring device 500 uses only the light-sensing component 531 of the light-sensing group 530, it means that in the “background-measuring phase” or in the “frequency-adjusting phase”, the distance-measuring device 500 does not need the switch SW₂₁ and the photo diode PD₂. Therefore, n the “background-measuring phase” or in the “frequency-adjusting phase”, the distance-measuring device 800 can operate as the distance-measuring device 500 by means of the light-sensing group 830. In addition, since in the detecting cycles T_(C1)˜T_(CN) of the “distance-calculating phase”, when the shutter periodic signal S_(ST1) represents “turning-on”, the shutter periodic signal S_(ST2) represents “turning-off”; when the shutter periodic signal S_(ST1) represents “turning-off”, the shutter periodic signal S_(ST2) represents “turning-on”. That is, the shutter periodic signals S_(ST1) and S_(ST2) do not represent “turning-on” at the same time. Thus, in the first-half cycles of the detecting cycles T_(C1)˜T_(CN) (the shutter periodic signal S_(ST1) represents “turning-on”), the distance-measuring device 800 can use the photo diode PD₁ of the light-sensing group 830 to accumulate electrons. When the shutter periodic signal S_(ST1) changes from “turning-on” to “turning-off”, the accumulated electrons of the photo diode PD₁ flows to the capacitor C₁ so as to change the voltage level of the voltage V_(C1). In the second-half cycles of the detecting cycles T_(C1)˜T_(CN) (the shutter periodic signal S_(ST2) represents “turning-on”), the distance-measuring device 800 can use the photo diode PD₁ of the light-sensing group 830 to accumulate electrons as well. When the shutter periodic signal S_(ST2) changes from “turning-on” to “turning-off”, the accumulated electrons of the photo diode PD₁ flows to the capacitor C₂ so as to change the voltage level of the voltage V_(C2). That is, although the light-sensing group 830 has only one photo diode PD₁, the light-sensing group 830 still can operate as the light-sensing group 530 in the “distance-calculating phase”. In other words, the distance-measuring device 800 can operate as the distance-measuring device 500 in the “distance-calculating phase”. In this way, since the distance-measuring device 800 can operate as the distance-measuring device 500 in the “background-measuring phase”, the “frequency-adjusting phase”, and the “distance-calculating phase”, the distance-measuring device 800 also can correctly measure the measured distance D by means of the methods of the “background-measuring phase”, the “frequency-adjusting phase”, and the “distance-calculating phase” mentioned in FIG. 2˜FIG. 4.

In addition, in the light-sensing group 530, the area occupied by the photo diode PD₂ is large. Hence, compared with the light-sensing group 530, the area occupied by the light-sensing group 830 is smaller, so that the cost of the light-sensing group 830 is lower.

Please refer to FIG. 10 and FIG. 11. FIG. 10 and FIG. 11 are diagrams illustrating a 3D image-sensing device 1000 of the present invention. The 3D image-sensing device 1000 comprises a distance-measuring device 1090 and a 2D image-sensing device 1100. The distance-measuring device 1090 comprises a light-emitting/sensing controlling circuit 1010, a light-emitting component 1020, a light-sensing module 1030, a distance-calculating circuit 1040, a background-calculating circuit 1050, a frequency-adjusting circuit 1060, and a focusing module 1070. The 2D image-sensing device 1100 comprises an image-sensing controlling circuit 1080, and the light-sensing module 1030, wherein the light-sensing module 1030 is shared by the 2D image-sensing device 1100 and the distance-measuring device 1090. The operation principle and the structure of the light-emitting/sensing controlling circuit 1010, the light-emitting component 1020, the distance-calculating circuit 1040, the background-calculating circuit 1050, the frequency-adjusting circuit 1060 are respectively similar to those of the light-emitting/sensing controlling circuit 110 (or the light-emitting/sensing controlling circuit 511), the light-emitting component 120 (or the light-emitting component 520 or 820), the distance-calculating circuit 140 (or the distance-calculating circuit 540 or 840), the background-calculating circuit 150 (or the background-calculating circuit 550 or 850), the frequency-adjusting circuit 160 (or the frequency-adjusting circuit 560 or 860). Compared with the distance-measuring devices 130, 500, and 800, the light-sensing module 1030 of the 3D image-sensing device 1000 comprises light-sensing groups CS₁˜CS_(M), wherein M represents a positive integer. The operation principle and the structure of the light-sensing groups CS₁˜CS_(M) are similar to those of the light-sensing group 130 or 530. In addition, the light-sensing groups CS₁˜CS_(M) are controlled by the image-sensing controlling circuit 1080 for sensing a scene P (as shown in FIG. 11) so as to obtain a 2D image SIM. The scene P comprises reflecting points PN₁˜PN_(M). The 2D image SIM comprises M pixels, and each pixel comprises two sub-pixels. The reflecting points PN₁˜PN_(M) of the scene P are respectively correspond to the M pixels of the 2D image SIM.

The 3D image-sensing device 1000 can use the image-sensing controlling circuit 1080 to control the light-sensing module 1030 sensing each reflecting point of the scene P so as to obtain the sub-pixel image data of the M pixels corresponding to reflecting points PN₁˜PN_(M). In addition, the 3D image-sensing device 1000 also can use the distance-measuring module 1090 to measure the distance between each reflecting point of the scene P and the 3D image-sensing device 1000. In other words, the 3D image-sensing device 1000 can obtain the 2D image SIM corresponding to the reflecting points PN₁˜PN_(M) and the distance data corresponding to the measured distances D₁˜D_(M) between the reflecting points PN₁˜PN_(M) and the 3D image-sensing device 1000.

For example, the structures of the light-sensing groups CS₁˜CS_(M) are similar to that of the light-sensing group 530. That is, each of the light-sensing groups CS₁˜CS_(M) comprises two light-sensing components. The light-sensing group CS₁ comprises light-sensing components CSA₁ and CSB₁; the light-sensing group CS₂ comprises light-sensing components CSA₂ and CSB₂; and the light-sensing group CS_(M) comprises light-sensing components CSA_(M) and CSB_(M) and so on. As a result, the 3D image-sensing device 1000 generates the shutter periodic signals S_(ST1) and S_(ST2), and the reading signal S_(RE) by means of the light-emitting/sensing controlling circuit 1010 of the distance-measuring device 1090 to control the light-sensing groups CS₁˜CS_(M). For example, the light-sensing group CS_(K) comprises light-sensing components CSA_(K) and CSB_(K). When the shutter periodic signal S_(ST1) represents “turning-on”, the light-sensing component CSA_(K) senses the energy of the reflected light L_(RD), which is generated by the reflecting point PN_(K) of the scene P reflecting the detecting light L_(ID), so as to accordingly accumulate the energy ERIK; when the shutter periodic signal S_(ST1) represents “turning-off”, the light-sensing component CSA_(K) does not sense the energy of the reflected light L_(RD) generated by the reflecting point PN_(K) of the scene P reflecting the detecting light L_(ID), and does not accumulate the energy E_(R1K). When the reading signal S_(RE) represents “reading”, the light-sensing component CSA_(K) outputs the light-sensing signal S_(LS1K) according to the accumulated energy E_(R1K). When the shutter periodic signal S_(ST2) represents “turning-on”, the light-sensing component CSB_(K) senses the energy of the reflected light L_(RD) generated by the reflecting point PN_(K) of the scene P reflecting the detecting light L_(ID), so as to accordingly accumulate the energy E_(R2K); when the shutter periodic signal S_(ST2) represents “turning-off”, the light-sensing component CSB_(K) does not sense the energy of the reflected light L_(RD) generated by the reflecting point PN_(K) of the scene P reflecting the detecting light L_(ID), and does not accumulate the energy E_(R2K). When the reading signal S_(RE) represents “reading”, the light-sensing component CSB_(K) outputs the light-sensing signal S_(LS2K) according to the accumulated energy E_(R2K). In addition, when the reading signal S_(RE) represents “reading”, the light-sensing components CSA_(K) and CSB_(K) reset the accumulated energy E_(R1K) and E_(R2K) after the light-sensing components CSA_(K) and CSB_(K) output the light-sensing signals S_(LS1K) and S_(LS2K).

In this way, the light-emitting/sensing controlling circuit 1010 respectively controls the light-sensing groups CS₁˜CS_(M) measuring the measured distances D₁˜D_(M) between the reflecting points PN₁˜PN_(M) of the scene P and the 3D image-sensing device 1000, by means of the methods of the “background-measuring phase” mentioned in FIG. 2, the “frequency-adjusting phase” mentioned in FIG. 4, and the “distance-calculating phase” mentioned in FIG. 3.

On the other hand, the 3D-image sensing device 1000 uses the image-sensing controlling circuit 1080 to control the light-sensing module 1030 sensing the reflecting points PN₁˜PN_(M) of the scene P to obtain the 2D image SIM, wherein the 2D image SIM comprises the sub-pixel image data G_(A1)˜G_(AM) and G_(B1)˜G_(BM). More particularly, the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSA₁ and CSB₁ sensing the reflecting point PN₁ of the scene P so as to obtain the two sub-pixel image data G_(A1) and G_(B1); the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSA_(X) and CSB_(X) sensing the reflecting point PN_(X) of the scene P so as to obtain the two sub-pixel image data G_(AX) and G_(BX), wherein the distance between the reflecting point PN_(X) and the 3D image-sensing device 1000 is D_(X); the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSA_(Y) and CSB_(Y) sensing the reflecting point PN_(Y) of the scene P so as to obtain the two sub-pixel image data G_(AY) and G_(BY), wherein the distance between the reflecting point PN_(Y) and the 3D image-sensing device 1000 is D_(Y); the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSA_(M) and CSB_(M) sensing the reflecting point PN_(M) of the scene P so as to obtain the two sub-pixel image data G_(AM) and G_(BM) and so on. In this way, the 3D image-sensing device 100 can construct a 3D image by means of the sub-pixel image data G_(A1)˜G_(AM) and G_(B1)˜G_(BM), and the distance data D₁˜D_(M).

In addition, the light-sensing groups CS₁˜CS_(M) of the light-sensing module 1030 are CMOS or CCD light sensors. That is, the structure and the principle of the light-sensing module 1030 are similar to those of the image-sensing module of the digital camera. In other words, when the 3D image-sensing device is applied in the digital camera, the digital camera can control the light-sensing module 1030 sensing the scene so as to obtain the 2D image by means of the image-sensing controlling circuit 1080 of the 3D image-sensing device 1000, and also can measure each distance between each reflecting point of the scene and the digital camera so as to obtain each distance data corresponding to each pixel by means of the distance-measuring device 1090 of the 3D image-sensing device 1000. In this way, the digital camera can construct a 3D image according to the distance data and the 2D image. Since the 2D image-sensing device 1100 and the distance-measuring device 1090 of the 3D image-sensing device 1000 share the light-sensing module 1030, the cost of constructing the 3D image is reduced.

For the distance-measuring device to more correctly calculate the measured distance, the present invention further provides a method of increasing signal-to-noise ratio of the distance-measuring device.

Please refer to FIG. 12. FIG. 12 is a diagram illustrating a method 1200 of increasing signal-to-noise ratio of the distance-measuring device according to an embodiment of the present invention. Please refer to FIG. 13. The method 1200 is applied for a distance-measuring device 1300. The distance-measuring device 1300 is utilized for measuring a measured distance D_(M) between a measured object MO and the distance-measuring device 1300. The distance-measuring device 1300 includes a light-emitting/sensing controlling circuit 1310, a distance-calculating circuit 1320, a light-emitting component LD, a focusing module LEN, and a light-sensing component CSU₁. The structures and the operational principles of the light-emitting component LD and the focusing module LEN are similar to those of the light-emitting components 120, 520, 820, and 1020, and the focusing modules 170, 570, and 870, respectively. The light-sensing component CSU₁ can be realized by the light-sensing component 531 (or 532). The light-sensing component CSU₁ senses and accumulates energy of light according to a shutter periodic signal S_(ST1), so as to generate a light-sensing signal S_(LS1). The steps of the method 1200 are illustrated as below:

-   step 1210: by means of the light-emitting periodic signal S_(LD),     the light-emitting/sensing controlling circuit 1310 controls the     light-emitting component LD to continuously emit a detecting light     L_(ID) to the measured object MO during an emitting period T_(LD)     for generating a reflected light L_(RD); -   step 1220: a delay period T_(DELAY) after the light-emitting     component LD starts to emit the detecting light L_(ID), the     light-emitting sensing controlling circuit 1310 switches the shutter     periodic signal S_(ST1) to represent “turning-on” during a sensing     period T_(SEN1) for the light-sensing component CSU₁ to sense and     accumulate energy of the reflected light L_(RD), and accordingly     generate the light-sensing signal S_(LS1); -   step 1230: the distance-calculating circuit 1320 obtains a time of     flight T_(TOF) of light going back and forth between the     distance-measuring device 1300 and the measured object MO according     to the light-sensing signal S_(LS1) and energy of the detecting     light L_(ID) emitted by the light-emitting component LD during the     emitting period T_(LD); -   step 1240: the distance-calculating circuit 1320 obtains the     measured distance D_(M) according to the time of flight T_(TOF), and     accordingly generates an output signal S_(OUT) for representing     length of the measured distance D_(M).

Please refer to FIG. 14. In the step 1210, by means of the light-emitting periodic signal S_(LD), the light-emitting/sensing controlling circuit 1310 controls the light-emitting component LD to continuously emit a detecting light L_(ID) to the measured object MO during an emitting period T_(LD) for generating a reflected light L_(RD). A time of flight T_(TOF) after the light-emitting component LD starts to emit the detecting light L_(ID), the reflected light L_(RD) reaches the light-sensing component CSU₁. The period length of the time of flight T_(TOF) is the sum of period lengths of the period of the detecting light L_(ID) emitted from the light-emitting component LD to the measured object MO and the period of the reflected light L_(RD) emitted from the measured object MO to the light-sensing component CSU₁. In other words, the period length of the time of flight T_(TOF) is equal to that of the period of light going back and forth between the distance-measuring device 1300 and the measured object MO.

In the step 1220, a delay period T_(DELAY) after the light-emitting component LD starts to emit the detecting light L_(ID), the light-emitting sensing controlling circuit 1310 switches the shutter periodic signal S_(ST1) to represent “turning-on” for a sensing period T_(SEN1). Thus, the light-sensing component CSU₁ senses and accumulates energy of light and accordingly generates the light-sensing signal S_(LS1). In addition, generally speaking, the range of length of the measured distance D_(M) is limited according to the application of the distance-measuring device 1300. In the present invention, the length of the measured distance D_(M) that the distance-measuring device 1300 can measure is limited to between a predetermined shortest measured distance D_(MIN) and a predetermined longest measured distance D_(MAX). For example, the distance-measuring device 1300 may be applied in a video game console. The distance-measuring device 1300 is disposed near a display device. The video game console detects the measured distance D_(M) between the user and the display device by means of the distance-measuring device 1300, and interacts with the user according to the measured distance D_(M). For example, the user plays a tennis game. When the measured distance D_(M) decreases, the player in the game controlled by the user moves forward; when the measured distance D_(M) increases, the player in the game controlled by the user moves backward. However, when the measured distance D_(M) between the display device and the user is too short (that is, the measured distance D_(M) is shorter than the predetermined shortest measured distance D_(MIN)), the user cannot see the whole image displayed by the display device and cannot easily play the tennis game. In other words, only when the measured distance D_(M) is longer than the predetermined shortest measured distance D_(MIN) is the measured distance D_(M) valid for the video game console to interact with the user. Since the measured distance D_(M) is longer than the predetermined shortest measured distance D_(M), in the step 1220, the light-emitting/sensing controlling circuit 1310 calculates the delay period T_(DELAY) according to the predetermined shortest measured distance D_(MIN) for ensuring that the reflected light L_(RD) reaches the light-sensing component CSU₁ after the delay period T_(DELAY). The light-emitting/sensing controlling circuit 1310 calculates the delay period T_(DELAY) according to the following formula: T _(DELAY)=2×D _(MIN) /C  (6).

Since the measured distance D_(M) is longer than the predetermined shortest measured distance D_(M), the time of flight T_(TOF) when the distance-measuring device 1300 measures the measured distance D_(M) is longer than the delay period T_(DELAY) calculated according to the formula (6). In other words, although the light-sensing component CSU₁ starts to sense the energy of the light a delay period T_(DELAY) after the light-emitting component LD starts to emit the detecting light L_(ID), the light-sensing component CSU₁ can still sense the reflected light L_(RD) in time.

In the step 1230, the light-sensing signal S_(LS1) can represent the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₁. In this way, the distance-calculating circuit 1320 can obtain the time of flight T_(TOF) of the light going back and forth between the distance-measuring device 1300 and the measured object MO, according to the ratio between the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₁ and the energy of the detecting light L_(ID) emitted by the light-emitting component LD during the emitting period T_(LD).

In the step 1240, since the time of flight T_(TOF) is the period of the light going back and forth between the distance-measuring device 1300 and the measured object MO, the distance-calculating circuit 1320 can calculate the measured distance D_(M) according to the following formula: D _(M) =T _(TOF) ×C/2  (7); wherein C represents speed of light. In this way, the distance-calculating circuit 1320 can generate the output signal S_(OUT) representing the length of the measured distance D_(M).

In the conventional method, the light-sensing component CSU₁ of the distance-measuring device 1300 starts to sense energy of light immediately after the light-emitting component LD starts to emit the detecting light L_(ID). In the step 1220 of the method 1200, the light-emitting sensing controlling circuit 1310 controls the light-sensing component CSU₁ to start to sense energy of light a delay period T_(DELAY) after the light-emitting component LD starts to emit the detecting light L_(ID). In this way, the light-emitting component CSU₁ does not sense the energy of the background light L_(B) (noise) during the delay period T_(DELAY). Therefore, the signal-to-noise ratio of the light-sensing signal S_(LS1) generated by the light-sensing component CSU₁ is improved. More particularly, provided that the light-sensing component CSU₁ stops sensing energy of light when the light-emitting component LD stops emitting detecting light L_(ID) (as shown in FIG. 14), in the conventional method, the energy E_(B) _(—) _(OLD) of the background light L_(B) sensed by the light-sensing component CSU₁ is proportional to the emitting period T_(LD), and the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₁ is E_(R) _(—) _(OLD). In the method 1200, the energy E_(B) _(—) _(NEW) of the background light L_(B) sensed by the light-sensing component CSU₁ is proportional to the sensing period T_(SEN1). Since the reflected light L_(RD) reaches the light-sensing component CSU₁ after the delay period T_(DELAY), the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₁ is still E_(R) _(—) _(OLD). Hence, the energy E_(B) _(—) _(NEW) is less than the energy E_(B) _(—) _(OLD). Compared with the signal-to-noise ratio (E_(R) _(—) _(OLD)/E_(B) _(—) _(OLD)) of the conventional method, the light-sensing signal S_(LS1) obtained by the method 1200 has a higher signal-to-noise ratio (E_(R) _(—) _(OLD)/E_(B) _(—) _(NEW)). In other words, the light-sensing signal S_(LS1) obtained by the method 1200 can more correctly represent the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₁. As a result, the time of flight T_(TOF) obtained in the step 1230 is more correct. In this way, a more correct measured distance D_(M) can be calculated in the step 1240.

In addition, in FIG. 14, the reflected light L_(RD) has to reach the light-sensing component CSU₁ before the end of the sensing period T_(SEN1) for the distance-measuring device 1300 to be capable of measuring the measured distance D_(M). That is, the period length of the time of flight T_(TOF) has to be shorter than the sum of period lengths of the sensing period T_(SEN1) and the delay period T_(DELAY). In other words, the predetermined longest measured distance D_(MAX) that the distance-measuring device can measure is represented by the following formula: D _(MAX)=2×(T _(SEN1) +T _(DELAY))/C  (8).

In addition, in FIG. 14, the sum of the period lengths of the sensing period T_(SEN1) and the delay period T_(DELAY) is equal to the period length of the emitting period T_(LD). That is, the light-emitting/sensing controlling circuit 1310 controls the light-sensing components CSU₁ to immediately stop sensing the energy of the reflected light L_(RD) when the light-emitting component LD stops emitting the detecting light L_(ID). However, the light-sensing components CSU₁ are not limited to immediately stop sensing the energy of the reflected light L_(RD) when the light-emitting component LD stops emitting the detecting light L_(ID). For example, please refer to FIG. 15. The light-emitting/sensing controlling circuit 1310 can set the period length of the sensing period T_(SEN1) equal to that of the emitting period T_(LD). It can be seen from formula (8) that since the sensing period T_(SEN1) increases, the predetermined longest measured distance D_(MAX) increases.

Please refer to FIG. 16. FIG. 16 is a diagram illustrating a method 1600 of increasing signal-to-noise ratio of the distance-measuring device according to another embodiment of the present invention. Please refer to FIG. 17. The method 1600 is applied for a distance-measuring device 1700. The distance-measuring device 1700 is utilized for measuring a measured distance D_(M) between a measured object MO and the distance-measuring device 1700. The distance-measuring device 1700 includes a light-emitting/sensing controlling circuit 1710, a distance-calculating circuit 1720, a light-emitting component LD, a focusing module LEN, and light-sensing components CSU₁ and CSU₂. The structures and the operational principles of the light-emitting component LD and the focusing module LEN are similar to those of the light-emitting components 120, 520, 820, and 1020, and the focusing modules 170, 570, and 870, respectively. The light-sensing components CSU₁ and CSU₂ can be realized by the light-sensing components 531 and 532. The light-sensing component CSU₁ senses and accumulates energy of light according to a shutter periodic signal S_(ST1), so as to generate a light-sensing signal S_(LS1). The light-sensing component CSU₂ senses and accumulates energy of light according to a shutter periodic signal S_(ST2), so as to generate a light-sensing signal S_(LS2). The steps of the method 1600 are illustrated as below:

-   step 1610: by means of the light-emitting periodic signal S_(LD),     the light-emitting/sensing controlling circuit 1710 controls the     light-emitting component LD to continuously emit a detecting light     L_(ID) to the measured object MO during an emitting period T_(LD)     for generating a reflected light L_(RD), -   step 1620: a delay period T_(DELAY) after the light-emitting     component LD starts to emit the detecting light L_(ID), the     light-emitting sensing controlling circuit 1610 switches the shutter     periodic signal S_(ST1) to represent “turning-on” during a sensing     period T_(SEN1) for the light-sensing component CSU₁ to sense and     accumulate energy of the reflected light L_(RD), and accordingly     generate the light-sensing signal S_(LS1); -   step 1630: when the light-sensing component CSU₁ stops sensing the     reflected light L_(RD), the light-emitting/sensing controlling     circuit 1710 switches the shutter periodic signal S_(ST2) to     represent “turning-on” during a sensing period T_(SEN2) for the     light-sensing component CSU₂ to sense and accumulate energy of the     reflected light L_(RD), and accordingly generate the light-sensing     signal S_(LS2); -   step 1640: the distance-calculating circuit 1720 obtains a time of     flight T_(TOF) of light going back and forth between the     distance-measuring device 1700 and the measured object MO according     to the ratio between the light-sensing signals S_(LS1) and S_(LS2); -   step 1650: the distance-calculating circuit 1720 obtains the     measured distance D_(M) according to the time of flight T_(TOF), and     accordingly generates an output signal S_(OUT) for representing     length of the measured distance D_(M).

Please refer to FIG. 18. In the step 1610, by means of the light-emitting periodic signal S_(LD), the light-emitting/sensing controlling circuit 1710 controls the light-emitting component LD to continuously emit a detecting light L_(ID) to the measured object MO during an emitting period T_(LD) for generating a reflected light L_(RD). A time of flight T_(TOF) after the light-emitting component LD starts to emit the detecting light L_(ID), the reflected light L_(RD) reaches the light-sensing component CSU₁. The time of flight T_(TOF) is equal to the period of light going back and forth between the distance-measuring device 1700 and the measured object MO.

In the step 1620, a delay period T_(DELAY) after the light-emitting component LD starts to emit the detecting light L_(ID), the light-emitting sensing controlling circuit 1710 switches the shutter periodic signal S_(ST1) to represent “turning-on” for a sensing period T_(SEN1). Thus, the light-sensing component CSU₁ senses and accumulates energy of light and accordingly generates the light-sensing signal S_(LS1). In the present embodiment, the length of the measured distance D_(M) that the distance-measuring device 1700 can measure is limited between the predetermined shortest measured distance D_(MIN) and the predetermined longest measured distance D_(MAX). Therefore, in the step 1620, the light-emitting/sensing controlling circuit 1710 calculates the delay period T_(DELAY) according to the formula (6) for the reflected light L_(RD) to reach the light-sensing component CSU₁ after the delay period T_(DELAY), so that the light-sensing component CSU₁ can sense the reflected light L_(RD) in time to generate a correct light-sensing signal S_(LS1). In addition, in FIG. 18, the reflected light L_(RD) still has to reach the light-sensing component CSU₁ before the end of the sensing period T_(SEN1) for the distance-measuring device 1700 to be capable of measuring the measured distance D_(M). That is, the period length of the time of flight T_(TOF) has to be shorter than the sum of period lengths of the sensing period T_(SEN1) and the delay period T_(DELAY). In other words, the predetermined longest measured distance D_(MAX) that the distance-measuring device can measure can still be represented by the formula (8).

In the step 1630, when the light-sensing component CSU₁ stops sensing the reflected light L_(RD), the light-emitting/sensing controlling circuit 1710 switches the shutter periodic signal S_(ST2) to represent “turning-on” for a sensing period T_(SEN2). Hence, in the sensing period T_(SEN2), the light-sensing component CSU₂ senses and accumulates the energy of the reflected light L_(RD), and accordingly generates the light-sensing signal S_(LS2).

In the step 1640, the light-sensing signal S_(LS1) represents the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₁. The light-sensing signal S_(LS2) represents the energy of the reflected light L_(RD) sensed by the light-sensing component CSU₂. According to the operational principle illustrated in FIG. 3, the distance-calculating circuit 1720 obtains the time of flight T_(TOF) of the light going back and forth between the distance-measuring device 1700 and the measured object MO according to the ratio between the light-sensing signals S_(LS1) and S_(LS2). More particularly, it can be seen from FIG. 18 that the time of flight T_(TOF) can be represented by the following formula:

$\begin{matrix} \begin{matrix} {T_{TOF} = {T_{DELAY} + T_{{SEN}\; 1} - {\left\lbrack {E_{R\; 1}/\left( {E_{R\; 1} + E_{R\; 2}} \right)} \right\rbrack \times T_{LD}}}} \\ {= {T_{DELAY} + T_{{SEN}\; 1} -}} \\ {\left\lbrack {\left( {S_{{LS}\; 1} - E_{B\; 1}} \right)/\left( {S_{{LS}\; 1} - E_{B\; 1} + S_{{LS}\; 2} - E_{B\; 2}} \right)} \right\rbrack \times {T_{LD}.}} \end{matrix} & (9) \end{matrix}$

When the distance-measuring device 1700 further includes a background-calculating circuit, the energy of the background light E_(B1) and E_(B2) can be calculated by means of the method illustrated in FIG. 2, so that the time of flight T_(TOF) can be calculated according to the formula (9). In addition, when the energy of the background light E_(B1) and E_(B2) is much less than the energy of reflected light E_(R1) and E_(R2), the formula (9) can be simplified to be the following formula: T _(TOF) =T _(DELAY) +T _(SEN1)−[(S _(LS1)/(S _(LS1) +S _(LS2))]×T _(LD)  (10).

In the step 1650, since the period length of the time of flight T_(TOF) is equal to that of the period of light going back and forth between the distance-measuring device 1700 and the measured object MO, the distance-calculating circuit 1720 can calculate the measured distance D_(M) according to the formula (7), and accordingly generates the output signal S_(OUT) representing the length of the measured distance D_(M).

Compared with the method 1200 illustrated in FIG. 12, in the method 1600, the time of flight T_(TOF) is calculated according to the ratio between the light-sensing signals S_(LS1) and S_(LS2). As a result, in the method 1600, the energy of the reflected light L_(R1) and L_(R2) can be repeatedly measured as shown in FIG. 18. When the energy of the reflected light L_(R1) and L_(R2) is measured N times, the light-sensing signals S_(LS11)˜S_(LS1N) and S_(LS21)˜S_(LS2N) are obtained. The distance-calculating circuit 1720 substitutes the light-sensing signal S_(LS1) obtained by accumulating the light-sensing signals S_(LS11)˜S_(LS1N) and the light-sensing signal S_(LS2) obtained by accumulating the light-sensing signals S_(LS21)˜S_(LS2N) into the formula (9) or (10) to calculate the time of flight T_(TOF). In this way, the measuring error due to the low energy of reflected light L_(RD) is reduced, so that the measured distance D_(M) is more correctly calculated in the step 1650.

In addition, in the method 1600, the duty cycle of the light-emitting component LD emitting the detecting light L_(ID) when the measured distance D_(M) is measured, namely the ratio between the emitting period T_(LD) and the detecting cycle T_(C), can be controlled by setting the period lengths of the sensing periods T_(SEN1) and T_(SEN2), and the emitting period T_(LD). For example, please refer to FIG. 19. The period length of detecting cycle T_(C) is set to be 2T_(LD). The period length of the sensing period T_(SEN1) and the sensing period T_(SEN2) are both equal to (T_(LD)−T_(DELAY)/2). In this way, the duty cycle of the light-emitting component LD emitting the detecting light L_(ID) is equal to 50%.

Based on the spirit of the methods 1200 and 1600, the present invention further provides a method 2000 for the distance-measuring device 100 of FIG. 1. Please refer to FIG. 20 and FIG. 21, which are diagrams illustrating the method 2000 of increasing the signal-to-noise ratio of the distance-measuring device 100. The steps of the method 2000 are illustrated as below:

-   step 2010: the light-emitting/sensing controlling circuit 110     switches the light-emitting periodic signal S_(LD) between     representing “turning-on” and “turning-off” with a detecting     frequency F_(C), for the light-emitting component 120 to emit the     detecting light L_(ID) to the measured object MO to generate a     reflected light L_(RD) during an emitting period T_(LD), and not     emit the detecting light L_(ID) during a non-emitting period     T_(NLD); -   step 2020: a delay period T_(DELAY) after every time the     light-emitting component 120 starts to emit the detecting light     L_(ID), the light-emitting/sensing controlling circuit 110 switches     the shutter periodic signal S_(ST1) to represent “turning-on” during     a sensing period T_(SEN1) for the light-sensing group 130 to sense     and accumulate energy of the reflected light L_(RD) to generate the     light-sensing signal S_(LS1); -   step 2030: the light-emitting/sensing controlling circuit 110     switches the shutter periodic signal S_(ST2) to represent     “turning-on” during a sensing period T_(SEN2) for the light-sensing     group 130 to sense and accumulate energy of the reflected light     L_(RD) to generate the light-sensing signal S_(LS2) after the     sensing period T_(SEN1); -   step 2040: the distance-calculating circuit 140 obtains a time of     flight T_(TOF) of light going back and forth between the     distance-measuring device 100 and the measured object MO according     to a ratio of the light-sensing signals S_(LS1) and S_(LS2); -   step 2050: the distance-calculating circuit 140 obtains the measured     distance MO according to the time of flight T_(TOF), and accordingly     generates an output signal S_(OUT) (not shown in FIG. 1)     representing the length of the measured distance D_(M).

Please refer to FIG. 21. The period of the distance-measuring device 100 measuring the measured distance D_(M) includes detecting cycles T_(C1)˜T_(CN). The period length of each detecting cycle T_(C1)˜T_(CN) is equal to (1/F_(C)). In the step 2010, the light-emitting/sensing controlling circuit 110 switches the light-emitting periodic signal S_(LD) between representing “turning-on” and “turning-off” with a detecting frequency F_(C), for the light-emitting component 120 to emit the detecting light L_(ID) to the measured object MO to generating a reflected light L_(RD) during the emitting period T_(LD) of each detecting cycle T_(C1)˜T_(CN), and not emit the detecting light L_(ID) during the non-emitting period T_(NLD) of each detecting cycle T_(C1)˜T_(CN). Thus, in each detecting cycle T_(C1)˜T_(CN), the measured object MO reflects the detecting light L_(ID) to generate reflected light L_(RD). More particularly, a time of flight T_(TOF) after the light-emitting component 120 starts to emit the detecting light LI_(D), the reflected light L_(RD) reaches the light-sensing group 130, wherein the time of flight T_(TOF) is equal to the period of light going back and forth between the distance-measuring device 100 and measured object MO.

In the step 2020, in each detecting cycle T_(C1)˜T_(CN), a delay period T_(DELAY) after every time the light-emitting component 120 starts to emit the detecting light L_(ID), the light-emitting/sensing controlling circuit 110 switches the shutter periodic signal S_(ST1) to represent “turning-on” during a sensing period T_(SEN1) for the light-sensing group 130 to sense and accumulate energy of the reflected light L_(RD) to generate the light-sensing signal S_(LS1). Provided that the measured distance D_(M) is limited to between the predetermined shortest measured distance D_(MIN) and the predetermined longest measured distance D_(MAX), in the step 2020, the light-emitting/sensing controlling circuit 110 calculates the delay period T_(DELAY) according to the formula (6) for the reflected light L_(RD) to reach the light-sensing component CSU₁ after the delay period T_(DELAY), so that the light-sensing component CSU₁ can sense the reflected light L_(RD) in time to generate a correct light-sensing signal S_(LS1). In addition, the reflected light L_(RD) still has to reach the light-sensing component CSU₁ before the end of the sensing period T_(SEN1) for the light-sensing group 130 to be capable of sensing the reflected light L_(RD). Hence, the predetermined longest measured distance D_(MAX) that the distance-measuring device can measure can still be represented by the formula (8).

In the step 2030, after the sensing period T_(SEN1) of each detecting cycle T_(C1)˜T_(CN), the light-emitting/sensing controlling circuit 110 switches the shutter periodic signal S_(ST2) to represent “turning-on” during a sensing period T_(SEN2). Hence, in the sensing period T_(SEN2), the light-sensing group 130 senses and accumulates the energy of the reflected light L_(RD), and accordingly generates the light-sensing signal S_(LS2). In addition, it can be seen in FIG. 21 that the light-emitting periodic signal S_(LD) and the shutter periodic signal S_(ST1) are approximately in phase (the only difference is the delay period T_(DELAY)), and the phase of the shutter periodic signal S_(ST1) (or the light-emitting periodic signal S_(LD)) is approximately opposite the phase of the second shutter periodic signal S_(ST2).

In the step 2040, the light-sensing signal S_(LS1) represents the energy of the reflected light L_(RD) sensed by the light-sensing group 130 in the sensing periods T_(SEN1). The light-sensing signal S_(LS2) represents the energy of the reflected light L_(RD) sensed by the light-sensing group 130 in the sensing periods T_(SEN2). Similar to the step 1640, the distance-calculating circuit 140 obtains the time of flight T_(TOF) of the light going back and forth between the distance-measuring device 100 and the measured object MO according to the ratio between the light-sensing signals S_(LS1) and S_(LS2). That is, in the step 2040, the distance-calculating circuit 140 can still calculate the time of flight T_(TOF) according to the formula (9).

In addition, since the distance-measuring device 100 can obtain the background signal S_(B), which represents the energy of background light L_(B) sensed by the light-sensing group 130 per unit time, by means of the method illustrated in FIG. 2, the energy of background light E_(B1) and E_(B2) in FIG. 21 can be calculated according to the following formulas: E _(B1) =S _(B) ×T _(SEN1)  (11); and E _(B2) =S _(B) ×T _(SEN2)  (12).

In this way, according to the formulas (9), (11), and (12), the time of flight T_(TOF) can be calculated by the following formula: T _(TOF) =T _(DELAY) +T _(SEN1)−[(S _(LS1) −S _(B) ×T _(SEN1))/(S _(LS1) −S _(B) ×T _(SEN1) +S _(LS2) −S _(B) ×T _(SEN2))]×T _(LD)  (13).

Therefore, from the formula (13), the distance-calculating circuit 140 can calibrate the ratio between the light-sensing signals S_(LS1) and S_(LS2) according to the background signal S_(B), and can obtain a more correct time of flight T_(TOF) according to the calibrated ratio between the light-sensing signals S_(LS1) and S_(LS2).

In the step 2050, since the time of flight T_(TOF) is equal to the period of the light going back and forth between the distance-measuring device 100 and the measured object MO, the distance-calculating circuit 140 can calculate the measured distance D_(M) according to the formulas (7) and (13), and accordingly generate the output signal S_(OUT) (not shown in FIG. 1) representing the length of the measured distance D_(M).

In conclusion, the method provided by the present invention is capable of increasing the signal-to-noise ratio of the distance-measuring device. The method provided by the present invention includes a light-emitting component emitting a detecting light to a measured object during an emitting period for generating a reflected light, a delay period after the light-emitting component emitting the detecting light, a light-sensing component sensing the energy of the reflected light so as to generate a light-sensing signal, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the energy of the detecting light and the light-sensing signal, and obtaining a measured distance between the distance-measuring device and the measured object according to the time of flight. Since the measured distance is larger than a predetermined shortest measured distance, the method can accordingly calculate a proper delay period for ensuring that the reflected light reaches the light-sensing component after the delay period. In this way, since the light-sensing component does not sense the background light during the delay period, the signal-to-noise ratio of the light-sensing signal is improved.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A method of increasing signal-to-noise ratio of a distance-measuring device, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device having a light-emitting component for emitting a detecting light, and a first light-sensing component for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, the method comprising: the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period; a delay period after the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal; obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the first light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period; and obtaining the measured distance according to the time of flight; wherein the delay period is calculated according to the predetermined shortest measured distance; wherein the delay period is calculated according to the following formula: T _(DELAY)=2×D _(MIN) /C; wherein T_(DELAY) represents the delay period; D_(MIN) represents the predetermined shortest measured distance; and C represents speed of light; wherein relationship between the predetermined longest measured distance and the first sensing period is represented by the following formula: D _(MAX)=2×(T _(SEN1) +T _(Delay))/C; wherein D_(MAX) represents the predetermined longest measured distance; and T_(SEN1) represents the first sensing period.
 2. The method of claim 1, wherein obtaining the measured distance according to the time of flight comprises: calculating the measured distance according to the following formula: D _(M) =T _(TOF) ×C/2; wherein D_(M) represents the measured distance; T_(TOF) represents the time of flight; and C represents speed of light.
 3. The method of claim 1, wherein a sum of period lengths of the first sensing period and the delay period is equal to period length of the emitting period.
 4. The method of claim 1, wherein period length of the first sensing period is equal to period length of the emitting period.
 5. A method of increasing signal-to-noise ratio of a distance-measuring device, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device having a light-emitting component for emitting a detecting light, a first light-sensing component for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and a second light-sensing component for sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal, the method comprising: the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period; a delay period after the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal; switching the second shutter periodic signal to represent turning-on during a second sensing period for the second light-sensing component to sense and accumulate energy of the reflected light to generate the second light-sensing signal when the first light-sensing component stops sensing the reflected light; obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal; and obtaining the measured distance according to the time of flight; wherein the delay period is calculated according to the predetermined shortest measured distance; wherein the delay period is calculated according to the following formula: T _(DELAY)=2×D _(MIN) /C; wherein T_(DELAY) represents the delay period; D_(MIN) represents the predetermined shortest measured distance; and C represents speed of light; wherein relationship between the predetermined longest measured distance and the first sensing period is represented by the following formula: D _(MAX)=2×(T _(SEN1) +T _(DELAY))/C; wherein D_(MAX) represents the predetermined longest measured distance; and T_(SEN1) represents the first sensing period.
 6. The method of claim 5, wherein obtaining the measured distance according to the time of flight comprises: calculating the measured distance according to the following formula: D _(M) =T _(TOF) ×C/2; wherein D_(M) represents the measured distance; T_(TOF) represents the time of flight; and C represents speed of light.
 7. The method of claim 5, wherein period length of the first sensing period is equal to period length of the second sensing period.
 8. A method of increasing signal-to-noise ratio of a distance-measuring device, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device having a light-emitting component for emitting a detecting light according to a light-emitting periodic signal, and a light-sensing group for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal, the method comprising: switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component to emit the detecting light to the measured object to generate a reflected light during an emitting period, and not emit the detecting light during a non-emitting period; a delay period after every time the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal; wherein the light-emitting periodic signal and the first shutter periodic signal are substantially in phase; switching the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal after the first sensing period; wherein phase of the light-emitting periodic signal is substantially opposite to phase of the second shutter periodic signal; obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal; and obtaining the measured distance according to the time of flight; wherein the delay period is calculated according to the predetermined shortest measured distance; wherein the delay period is calculated according to the following formula: T _(DELAY)=2×D _(MIN) /C; wherein T_(DELAY) represents the delay period; D_(MIN) represents the predetermined shortest measured distance; and C represents speed of light; wherein relationship between the predetermined longest measured distance and the first sensing period is represented by the following formula: D _(MAX)=2×(T _(SEN1) +T _(DELAY))/C; wherein D_(MAX) represents the predetermined longest measured and T_(SEN1) represents the first sensing period.
 9. The method of claim 8, wherein obtaining the measured distance according to the time of flight comprises: calculating the measured distance according to the following formula: D _(M) =T _(TOF) ×C/2; wherein D_(M) represents the measured distance; T_(TOF) represents the time of flight; and C represents speed of light.
 10. The method of claim 8, further comprising: switching the first shutter periodic signal to represent turning-on during a background-measuring phase, for the light-sensing group to sense and accumulate energy of a background light to generate the first light-sensing signal; and generating a background signal according to the first light-sensing signal generated by the light-sensing group during the background-measuring phase and period length of the first shutter periodic signal representing turning-on during the background-measuring phase.
 11. The method of claim 10, wherein obtaining the time of flight of light going back and forth between the distance-measuring device and the measured object according to the ratio of the first light-sensing signal and the second light-sensing signal comprises: calibrating the ratio between the first light-sensing signal and the second light-sensing signal according to the background signal; and obtaining the time of flight of light going back and forth between the distance-measuring device and the measured object according to the calibrated ratio between the first light-sensing signal and the second light-sensing signal.
 12. The method of claim 11, wherein obtaining the time of flight of light going back and forth between the distance-measuring device and the measured object according to the calibrated ratio between the first light-sensing signal and the second light-sensing signal comprises: calculating the time of flight according to the following formula: T _(TOF) =T _(DELAY) +T _(SEN1)−[(S _(LS1) −S _(B) ×T _(SEN1))/(S _(LS1) −S _(B) ×T _(SEN1) +S _(LS2) −S _(B) ×T _(SEN2))]×T _(LD); wherein T_(TOF) represents the time of flight; T_(DELAY) represents the delay period; T_(SEN1) represents the first light-sensing period; T_(SEN2) represents the second light-sensing period; S_(B) represents the background signal; S_(LS1) represents the first light-sensing signal; S_(LS2) represents the second light-sensing signal; and T_(LD) represents the emitting period.
 13. A distance-measuring device with increased signal-to-noise ratio, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device comprising: an emitting component, for emitting a detecting light; a first light-sensing component, for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal; a light-emitting/sensing controlling circuit, for controlling the emitting component to continuously emit the detecting light to the measured object to generate a reflected light during an emitting period, and a delay period after the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switching the first shutter periodic signal representing turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance; and a distance-calculating circuit, for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the first light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period, and generating an output signal representing length of the measured distance according to the time of flight; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the following formula: T _(DELAY)=2×D _(MIN) /C; wherein T_(DELAY) represents the delay period; D_(MIN) represents the predetermined shortest measured distance; and C represents speed of light; wherein relationship between the predetermined longest measured distance and the first sensing period is represented by the following formula: D _(MX)=2×(T _(SEN1) +T _(DELAY))/C; wherein D_(MAX) represents the predetermined longest measured distance; and T_(SEN1) represents the first sensing period.
 14. The distance-measuring device of claim 13, wherein the distance-calculating circuit calculates the measured distance according to the following formula: D _(M) =T _(TOF) ×C/2; wherein D_(M) represents the measured distance; T_(TOF) represents the time of flight; and C represents speed of light.
 15. The distance-measuring device of claim 13, wherein a sum of period lengths of the first sensing period and the delay period is equal to period length of the emitting period.
 16. The distance-measuring device of claim 13, wherein period length of the first sensing period is equal to period length of the emitting period.
 17. The distance-measuring device of claim 13, further comprising: a focusing module, for focusing the reflected light onto the first light-sensing component.
 18. A distance-measuring device with increased signal-to-noise ratio, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device comprising: an emitting component, for emitting a detecting light; a first light-sensing component, for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal; a second light-sensing component, for sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal; a light-emitting/sensing controlling circuit, for controlling the emitting component to continuously emit the detecting light to the measured object to generate a reflected light during an emitting period, and a delay period after the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switching the first shutter periodic signal representing turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal, and when the first light-sensing component stops sensing the reflected light, the light-emitting/sensing controlling circuit switching the second shutter periodic signal representing turning-on during a second sensing period for the second light-sensing component to sense and accumulate energy of the reflected light to generate the second light-sensing signal; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance; and a distance-calculating circuit, for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing length of the measured distance according to the time of flight; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the following formula: T _(DELAY)=2×D _(MIN) /C; wherein TDELAY represents the delay period; DMIN represents the predetermined shortest measured distance; and C represents speed of light; wherein relationship between the predetermined longest measured distance and the first sensing period is represented by the following formula: D _(MAX)=2×(T _(SEN1) +T _(DELAY))/C; wherein D_(MAX) represents the predetermined longest measured distance; and T_(SEN1) represents the first sensing period.
 19. The distance-measuring device of claim 18, wherein the distance-calculating circuit calculates the measured distance according to the following formula: D _(M) =T _(TOF) ×C/2; wherein D_(M) represents the measured distance; T_(TOF) represents the time of flight; and C represents speed of light.
 20. The distance-measuring device of claim 18, wherein period length of the first sensing period is equal to period length of the second sensing period.
 21. The distance-measuring device of claim 18, further comprising: a focusing module, for focusing the reflected light onto the first light-sensing component and the second light-sensing component.
 22. A distance-measuring device with increased signal-to-noise ratio, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device comprising: an emitting component, for emitting a detecting light; a light-sensing group, for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal; a light-emitting/sensing controlling circuit, for switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component to emit the detecting light to the measured object to generate a reflected light during an emitting period, and not emit the detecting light during a non-emitting period; wherein a delay period after every time the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal, and after the first sensing period, the light-emitting/sensing controlling circuit switches the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal; wherein the light-emitting periodic signal and the first shutter periodic signal are substantially in phase, and phase of the light-emitting periodic signal is substantially opposite phase of the second shutter periodic signal; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance; and a distance-calculating circuit, for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing length of the measured distance according to the time of flight; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the following formula: T _(DELAY)=2×D _(MIN) /C; wherein T_(DELAY) represents the delay period; D_(MIN) represents the predetermined shortest measured distance; and C represents speed of light; wherein relationship between the predetermined longest measured distance and the first sensing period is represented by the following formula: D _(MAX)=2×(T _(SEN1) +T _(DELAY))/C; wherein D_(MAX) represents the predetermined longest measured distance; and T_(SEN1) represents the first sensing period.
 23. The distance-measuring device of claim 22, wherein the distance-calculating circuit calculates the measured distance according to the following formula: D _(M) =T _(TOF) ×C/2; wherein D_(M) represents the measured distance; T_(TOF) represents the time of flight; and C represents speed of light.
 24. The distance-measuring device of claim 22, further comprising: a focusing module, for focusing the reflected light onto the light-sensing group.
 25. The distance-measuring device of claim 22, further comprising: a background-calculating circuit, the light-emitting/sensing controlling circuit switching the first shutter periodic signal to represent turning-on during a background-measuring phase for the light-sensing group to sense and accumulate energy of a background light to generate the first light-sensing signal, the background-calculating circuit generating a background signal according to the first light-sensing signal generated by the light-sensing group during the background-measuring phase and period length of the first shutter periodic signal representing turning-on during the background-measuring phase.
 26. The distance-measuring device of claim 25, wherein the distance-calculating circuit calibrates the ratio between the first light-sensing signal and the second light-sensing signal according to the background signal, and obtains the time of flight of light going back and forth between the distance-measuring device and the measured object according to the calibrated ratio between the first light-sensing signal and the second light-sensing signal.
 27. The distance-measuring device of claim 26, wherein the distance-calculating circuit calculates the time of flight according to the following formula: T _(TOF) =T _(DELAY) +T _(SEN1)−[(S _(LS1) −S _(B) ×T _(SEN1))/(S _(LS1) −S _(B) ×T _(SEN1) +S _(LS2) −S _(B) ×T _(SEN2))]×T _(LD); wherein T_(TOF) represents the time of flight; T_(DELAY represents) the delay period, T_(SEN1) represents the first light-sensing period; T_(SEN2) represents the second light-sensing period; S_(B) represents the background signal; S_(LS1) represents the first light-sensing signal; S_(LS2) represents the second light-sensing signal; and T_(LD) represents the emitting period.
 28. A method of increasing signal-to-noise ratio of a distance-measuring device, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device having a light-emitting component for emitting a detecting light according to a light-emitting periodic signal, and a light-sensing group for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal, the method comprising: switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component to emit the detecting light to the measured object to generate a reflected light during an emitting period, and not emit the detecting light during a non-emitting period; a delay period after every time the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal; wherein the light-emitting periodic signal and the first shutter periodic signal are substantially in phase; switching the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal after the first sensing period; wherein phase of the light-emitting periodic signal is substantially opposite to phase of the second shutter periodic signal; obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal; obtaining the measured distance according to the time of flight; switching the first shutter periodic signal to represent turning-on during a background-measuring phase, for the light-sensing group to sense and accumulate energy of a background light to generate the first light-sensing signal; and generating a background signal according to the first light-sensing signal generated by the light-sensing group during the background-measuring phase and period length of the first shutter periodic signal representing turning-on during the background-measuring phase; wherein the delay period is calculated according to the predetermined shortest measured distance.
 29. The method of claim 28, wherein obtaining the time of flight of light going back and forth between the distance-measuring device and the measured object according to the ratio of the first light-sensing signal and the second light-sensing signal comprises: calibrating the ratio between the first light-sensing signal and the second light-sensing signal according to the background signal; and obtaining the time of flight of light going back and forth between the distance-measuring device and the measured object according to the calibrated ratio between the first light-sensing signal and the second light-sensing signal.
 30. The method of claim 29, wherein obtaining the time of flight of light going back and forth between the distance-measuring device and the measured object according to the calibrated ratio between the first light-sensing signal and the second light-sensing signal comprises: calculating the time of flight according to the following formula: T _(TOF) =T _(DELAY) +T _(SEN1)−[(S _(LS1) −S _(B) ×T _(SEN1))/(S _(LS1) −S _(B) ×T _(SEN1) +S _(LS2) −S _(B) ×T _(SEN2))]×T _(LD); wherein T_(TOF) represents the time of flight; T_(DELAY) represents the delay period; T_(SEN1) represents the first light-sensing period; T_(SEN2) represents the second light-sensing period; S_(B) represents the background signal; S_(LS1) represents the first light-sensing signal; S_(LS2) represents the second light-sensing signal; and T_(LD) represents the emitting period.
 31. A distance-measuring device with increased signal-to-noise ratio, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device comprising: an emitting component, for emitting a detecting light; a light-sensing group, for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal; a light-emitting/sensing controlling circuit, for switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component to emit the detecting light to the measured object to generate a reflected light during an emitting period, and not emit the detecting light during a non-emitting period; wherein a delay period after every time the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal, and after the first sensing period, the light-emitting/sensing controlling circuit switches the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal; wherein the light-emitting periodic signal and the first shutter periodic signal are substantially in phase, and phase of the light-emitting periodic signal is substantially opposite phase of the second shutter periodic signal; wherein the light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance; a distance-calculating circuit, for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing length of the measured distance according to the time of flight; and a background-calculating circuit, the light-emitting/sensing controlling circuit switching the first shutter periodic signal to represent turning-on during a background-measuring phase for the light-sensing group to sense and accumulate energy of a background light to generate the first light-sensing signal, the background-calculating circuit generating a background signal according to the first light-sensing signal generated by the light-sensing group during the background-measuring phase and period length of the first shutter periodic signal representing turning-on during the background-measuring phase.
 32. The distance-measuring device of claim 31, wherein the distance-calculating circuit calibrates the ratio between the first light-sensing signal and the second light-sensing signal according to the background signal, and obtains the time of flight of light going back and forth between the distance-measuring device and the measured object according to the calibrated ratio between the first light-sensing signal and the second light-sensing signal.
 33. The distance-measuring device of claim 32, wherein the distance-calculating circuit calculates the time of flight according to the following formula: T _(TOF) =T _(DELAY) +T _(SEN1)−[(S _(LS1) −S _(B) ×T _(SEN1))/(S _(LS1) −S _(B) ×T _(SEN1) +S _(LS2) −S _(B) ×T _(SEN2))]×T _(LD); wherein T_(TOF) represents the time of flight; T_(DELAY represents) the delay period, T_(SEN1) represents the first light-sensing period; T_(SEN2) represents the second light-sensing period; S_(B) represents the background signal; S_(LS1) represents the first light-sensing signal; S_(LS2) represents the second light-sensing signal; and T_(LD) represents the emitting period. 